1. Technical Field
The invention relates to preventing the unauthorized use of a device comprising a display, especially a valuable computer display, such as a flat display device.
2. Discussion of Related Art
Thefts of personal computer equipment constitute a significant problem, because especially the new flat display devices are light, small and valuable. Mechanical means for preventing thefts include, for instance, fastening the devices with wire ropes, but this method is clumsy and not even very efficient, because wire ropes can be cut by equipment generally used by thieves. The solutions presented in the following are electric means for preventing the theft or unauthorized use of the device.
Protection against theft of personal computers connected to a Local Area Network (LAN) is known from the patent specification JP-09027087. In this solution, the devices form a closed circuit, the breaking of which causes the alarm to go off. If the device is stolen in spite of the alarm, information of this is transmitted to the theft notification device via the telephone line.
In another well-known method a password is requested always when the device is switched on in mobile stations and car radios. There is also a method used in computers, in which password request is activated when the display device is switched to a display saving mode.
The known solutions have the problem that the arrangement is unpractical or complicated. The problem in the password-requesting systems is a frequent need to enter the password. The known electric solutions have the drawback that the display device is not protected, because usually only the use of information in the computer is restricted.
It is the object of the invention to provide a solution for limiting the use of the display device, which solution does not require entering the password every time when the display device is switched to the normal operating mode, but which protects especially the display device and does not only prevent the use of the processor unit of the computer.
The invention relates to a method for limiting the use of a display device, which display device is detachable from the equipment that controls it. In accordance with the invention, the detachment of the display device is examined and the length of time during which the display device is detached is measured, in order to limit the use of the display device on the basis of a certain predetermined time limit.
The invention also relates to an arrangement for limiting the use of a display device, which display device is detachable from the equipment that controls it. The arrangement in accordance with the invention comprises a detachment detector for examining the detachment of the display device and for measuring the period of time during which the display device is detached, for limiting the use of the display device on the basis of a certain predetermined time limit.
The invention also relates to a display device which can be detached from the equipment controlling the display device, and which comprises means for limiting the use of the display device. In accordance with the invention, the display device comprises
a coupling for connecting the display device to the equipment controlling the display device,
a detector circuit for detecting the detachment of the processor unit,
a line connection from the processor unit for entering information, such as a password,
a processor for controlling the prevention mode on the basis of a signal given by the detector circuit,
a display screen and controller for dealing with the prevention mode and the password, and
a non-volatile memory for saving the password.
The activation of the prevention mode of the display device is based on the breaking of the electrical connection from the device environment. In accordance with the invention, the prevention mode is not activated if the connection is not broken for a certain period of time that can be set in advance, for example. In this way, the normal use of the display device is not made more difficult, but unauthorized use of the device is prevented in case of a theft, for example. The breaking of the connection takes place e.g. from a device that controls the display device, such as a processor unit, a Local Area Network (LAN) or a Wide Area Network (WAN). The activation of the prevention mode is primarily based on the state of a mechanical or electrical switch after detachment of the connection cable. An electric switch or a circuit which detects the detachment can react at least to a break in the electrical connection, the lack of a signal or the end of the connection in the local area network.
The invention can also be applied to a display device connected wirelessly and equipped with a circuit which detects a break in the wireless connection. A wireless connection like this is, for example, an Infra Red (IR) or Radio Frequency (RF) link. The connection break is recognized by monitoring the traffic between the display device and the use environment, the ending of which or the lack of a signal is a criterion for recognizing a break.
The circuit which detects the detachment in accordance with the invention gives the processor of the display device information for locking the display device after a certain period from the detachment. This period of time can vary from a few seconds to days. During the time when the display device is locked, only a limited series of functions is operational, including at least the functions required for the request and entry of the password. The request for password takes place in a small window on the display, for example, whereby the name and address of the owner can also be displayed. The passwords can include, at least, the password given by the user and/or a basic password possibly derived from the serial number, which can be solved by the maintenance service. In addition, the password can be saved in the memory as coded for high-level security. In this connection, high-level security means security which is especially difficult to break by criminal means. Consecutive trials of a password can be limited by a prevention period between password entries.
These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing.